What really should be my star?

My birth date is 14 July 1997 or that's what i believed for a good part of my life , and i thought that my star is cancer but a year or more back in the past , my parents told me that they adopted me and my real birth date was 10 September , and now i am quite baffled what actually could be my zodiac sign? I just want to ask you people that should i keep thinking i am cancer star or i should stick to my real birthdate star? :P